Doom source code
The Doom source code was released December 23, 1997, initially under a not-for-profit license. Later, permission was granted to re-release the source code under the GNU GPL in October 3, 1999.
Before release, the source code was tidied up by Bernd Kreimeier; the source release includes a changelog of his contributions. Several documentation files are also included. The original plan for the source code release involved a book Kreimeier was to write on the Doom engine; however, due to Doom's decreasing relevance in the gaming community, it was eventually judged not to be a marketable idea, and the project was abandoned. The source code was then released to the public.
Because of legal issues regarding the DMX sound library developed by Paul Radek which was used for Doom, the release was of the source code to the Linux port of Doom. Despite this, within several months, several ports had been made back to DOS. As a result, many source ports exist.
Source code structure
The source code can be divided into sections. Files and functions within the source code have one- or two-letter prefixes to denote their subsystem.
A detailed list of files and their purposes can be found in Doom source code files.